Check valves are used in a variety of applications to limit flow in one direction while allowing flow in an opposite direction. Typically two way check valves are used to prevent flow in opposed directions when actuated but having been actuated they remain closed to flow in both directions. Some examples of these types of valves are: US2012/0222861 and U.S. Pat. No. 4,628,996 (FIGS. 11 and 12). Other designs just cut off flow in multiple directions when there is a line break such as U.S. Pat. No. 5,547,029. Some designs use redundant check valves in parallel that interact such as U.S. Pat. No. 6,659,184 FIG. 2. Yet other designs are mainly one way check valves but mention in passing that they could be configured as two way check valves without describing how that would be usefully accomplished in the context of their disclosure such as US2013/0255952. Yet other designs are multidirectional valves that redirect flow in various flow regimes and are not necessarily check valves at all such as U.S. Pat. No. 7,658,229.
In some applications there is a need to build pressure in a downhole direction such as for setting a packer and then having set the packer to convert to a unidirectional check valve operation where flow is permitted in the downhole direction but prevented in the uphole direction. In a specific application, a heavy oil that needs to be diluted so that it can be pumped to the surface with an electric submersible pump (ESP) requires the ability to pump down the diluent in a downhole direction while providing a safety device that will prevent flow backing up the diluent delivery line should the formation experience a pressure buildup. At the same time a packer needs to be set to isolate the heavy oil from the remainder of the borehole so that mixing with the diluent can happen below the packer. The present invention address this specific situation and is suitable for other applications where for a time single direction checking of flow is desired such as to set a packer and at other times flow is enabled in a direction previously checked to accomplish another downhole objective such as fluid dilution of a heavy oil so it can be pumped to the surface with an ESP. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.